Rheostat



April 24, 1934. G', B, CROUSE 1,955,906

RHEosTAT Filed June 18, 1930 '26 za /6 /f L75 INVENTOR @e0/'ya B.fraz/sa BY ff-a g ATTO E Patented Apr. 24, 1934 UNITED STATES PATENTOFFICE Hardwick llindle, Inc.,

ration of New Jersey Newark, N. J., a corpo- Application June 18, 1930,Serial No. 461,975

3 Claims.

This invention relates to rheostats particularly of the type having asliding contact device adapted to be moved over a suitable resistancewire wound on a tubular member, provision being made for bothcoarse andfine adjustments of the contact device.

In rheostats of this type as heretofore constructed the fine adjustmentof the contact device is obtained by a connection between it and arotatable rod provided with a screw thread, the device being slidablymounted upon a guide rod placed parallel to the rotatable rod. Forcoarse adjustment whereby the contact device may be moved rapidly fromone position to another, the connection to the threaded rod is of adetachable nature to permit it to be disengaged from the rod whendesired. It is arranged to be held out of engagement with the rod oreven locked in its disengaged position, while the contact device isbeing moved from one position to another. In the first case it isusually necessary to use both hands to manipulate the device, while inthe latter case, the initial disengaging and locking operations mustfirst be performed by manipulation of the devices provided for thispurpose and then one must take hold of the entire contact device toalter its position.

Furthermore in such prior rheostats the contact device includes movableleaf springs which are attached to the device and the resiliency ofwhich is depended upon te hold them against the wire with suilicientpressure to make good electrical contact. This resiliency is not howeverconstant for the springs carry current and therefore become heated andgradually lose their resiliency. The leaves of the springs are flexiblein the direction of movement of the contact device so that as the deviceis moved the leaves are deected and catch on the wire possible danger ofdamaging it or even breaking it.

The present invention has for its general object the provision of arheostat in which the disadvantages of prior devices, particularly withrespect to the contact device, are overcome, whereby it may be morequickly and conveniently manipulated when a coarse adjustment is desiredand then by only one hand. The contact springs are movably mounted onthe device and are held against the wire of the rheostat by othersprings which do not carry current and therefore are not subject tochanges in their resiliency. In other words, the functions of contactmaking and application of pressure to the springs are separated. Thisarrangement also avoids the tendency of the free ends of the contactsprings to catch on the wire as the contact device is moved over it.

A further improvement resides in an arrangement for fastening in placethe ends of the resistance wire and attaching thereto the wires of theexternal circuit.

The particular nature of the invention as well as other objects andadvantages thereof will appear most clearly from a description of apreferred embodiment as shown in the accompanying drawing in which Fig.1 is an elevation partly in section of the rheostat,

Fig. 2 is a plan View of the rheostat,

Fig. 3 is a transverse sectional view taken along the lines 33 of Figs.1 and 2, and

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3.

The resistance unit of the device consists of a cylindrical tube 1 of asuitable heat resisting and electrically insulating material, such asporcelain. The tube is wound with wire 2 of the desired resistance andcurrent carrying capacity for the circuit in which the rheostat is to beused. The insulation of the wire is formed by suitable oxidization ofits surface. The wire is wound under the maximum tensile strength whichthe material will stand and at a slight angle to the axis of the tube sothat the turns are snugly wedged together but insulated from each otherby the oxide coating which however becomes worn oif in the path of thebrushes of the contact device so that no resistance is interposedbetween the wire and the brushes.

The ends of the wire are held in place by bands 3 wide enough to embraceseveral turns of the wire at each end of the unit. As shown most clearlyin Fig. 3, the ends of each band are turned outwardly and provided withshoes 4 and 5 preferably Welded to the ends and having their inner edgesshaped to conform to the bends of the bands at these points. A clampingscrew 6 passes through the upper shoe 4 and is threaded into the lowershoe 5. The upper shoe is provided with a threaded extension 7 on whicha pair of binding nuts 8 are screwed by which connection to the externalcircuit may be made.

The resistance unit is mounted between two end brackets 9 and l0 whichserve as supports for the rheostat. The brackets are clamped against theends of the tube 2 by a solid rod 11 having nuts 12 at its ends and ahollow rod 13 which is internally threaded for the reception of clampingscrews 14. The hollow rod also serves as a guide for the contact deviceof the rheostat and for this purpose it must be insulated from thebrackets 9 and 10. This is accomplished by means of insulating washers15 and bushings 16. In order to allow for slight changes in the relativelengths of the tube and the rods when the rheostat becomes heated underload soft asbestos washers 17 are placed between the ends of the tubeand the corresponding brackets 9 and 10.

In order to eliminate the necessity for accurately matching the lengthof the rod 13 to the length of the tube 1, the rod is made shorter thanthe tube and shimmed out to the correct length by washers 18. One of theclamping screws 14 is provided with a threaded extension 19 whichcarries a pair of binding nuts 20 for connection to an external circuit.

The outer surface of the hollow rod 13 is machined and carries a sleeve21 which is accurately machined to slide freely on the rod, thusavoiding any appreciable lost motion between the rod and the elements ofthe Contact device which are mounted on the sleeve, such as occurs inprior rheostats of this general type in which machined parts are notused and springs or other devices are provided for taking up the lostmotion between the parts.

The sleeve 2l serves to carry the elements of the contact device. Thefirst of these is a member 22 provided with a pair of spaced lugs 23which are machined to accurately t the sleeve 21. A corresponding member24 is provided with a pair of spaced lugs 25 also accurately machined tofit the sleeve. Attached to the tops of the lugs 25 by screws 26 is aknob 27 formed of suitable insulating material, preferably in one piece.The lower flange 28 of the knob is provided with an aperture 29 throughwhich passes a lever 30 having at one side an extension 3l lying betweenthe lugs 25 and provided with an aperture through which the sleeve 21passes. The upper end of the lever is normally forced outwardly by acoiled spring 32 having its ends set in recesses in the lever and thecentral portion or rib of the knob.

In assembling the device, one end of the sleeve 21 is initially spunoutwardly to form a slight flange 33. The sleeve is then passed throughthe lugs 23 and 25 and the aperture in the extension 31, after which theother end of the sleeve is also spun outwardly to form a correspondingflange to retain the members 22 and 24 and the lever 30 in place on thesleeve.

The lower end of the lever 30 carries a pin 34 which under the influenceof spring 32 normally enters the thread of a screw 35 mounted in holesin the end brackets 9 and 10, one end of the screw being provided with aknob 36 by which the screw may be rotated to shift the contact devicealong the rod 13. Washers 37 are employed for preventing end play of thescrew without the necessity of forming the screw to fit accuratelybetween the end brackets.

Each of the members 22 and 24 is provided on the inner face of itsdepending portion with inwardly extending die cast rivets 38 which serveto hold in place a Contact spring 39 which as shown most clearly in Fig.3 has a rounded projection 40 at its lower end which engages the wire 2of the resistance unit and an inwardly extending portion 4l at its upperend. A pair of curved springs 42 are sprung into place beneath the lugsof the members 22 and 24, with their ends bearing against the portions41 of the contact springs 39, whereby the latter are held firmly againstthe wire 2 on account of the rotary connection between the sleeve 21 andthe members 22 and 24 to which the springs are attached which permitsthe springs 42 to force the contact springs inwardly against the wire.The ends of the springs 42 are turned upwardly as indicated at 43 toform rounded surfaces for engaging the portions 41 of the contactsprings to produce most satisfactory operation.

For the usual fine adjustments of the contact device the elements of thelatter occupy the positions shown in the drawing, that is, with the pin34 held in engagement with the thread of the screw 35 by the effect ofthe spring 32 pressing outwardly the upper end of the lever. When thescrew is rotated by the knob 36 the contact device will be translatedalong the wire 2 to vary the resistance of the rheostat as may bedesired.

When however a coarse adjustment is desired, the operator takes hold ofthe knob 27 and with the thumb or a iinger of the same hand pressesinwardly the upper end of the lever 30, thus disengaging the pin 34 fromthe screw 35 so that he may quickly move the contact device from oneposition to another. Thereafter by releasing the lever the normalcondition of the apparatus is restored so that the contact device may bemore accurately adjusted to the desired position.

While the apparatus of the invention has been referred to as a rheostatit will be understood that it is equally adapted to be used as apotentiometer, or for any purpose for which apparatus of this charactermay be used, by appropriately arranging the circuit connections. It willalso be understood that while a preferred embodiment of the inventionhas been shown, it may be embodied in other forms and that variouschanges in structural details may be made Without departing from theprinciple of the invention as defined in the appended claims.

I claim:

1. In a rheostat, the combination of a resistance unit, a rod parallelto the axis of the unit, a member slidably mounted on the rod, a pair ofdevices rotatably mounted on the member, a contact element attached toeach of the devices, a spring bearing at its centre against parts of thedevices beneath the slidable member and at its ends against the cuterportions of said devices to hold the contact elements against theresistance unit and means associated with the slidable member and thedevices for translating the contact elements with respect to theresistance unit.

2. In a rheostat, the combination of a resistance unit, a rod parallelto the axis of the unit, a contact device slidably mounted on the rodand co-acting with the unit, a screw parallel to the rod, a knob mountedon the device in fixed relation thereto, a lever movably mounted on thedevice and having its upper end adjacent to the knob, and its lower endadjacent to the screw,

a pin connected to the lower end of the lever,

a spring between the upper end of the lever and the knob for normallypressing the pin into engagement with the screw, whereby the contactdevice may then be translated by rotation of the screw or be movedrapidly from one position to another by simultaneous manipulation of theknob and disengagement of the pin and screw by pressure of the upper endof the lever against the spring.

3. In a rheostat, the combination of a resistlugs and their ends bearingagainst the extended portions of the devices to hold the Contactelements against the resistance unit and means associated with thesleeve for translating it and the devices and elements mounted thereonwith respect to the resistance unit.

GEORGE B. CROUSE.

